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Monitoring playa water resources using gis and remote sensing
 

Monitoring playa water resources using gis and remote sensing

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Teresa Stephens, GIS Specialist, Paul Bechtel & Associates, Inc. and Andrew Weinberg, Geoscientist, Texas Water Development Board

Teresa Stephens, GIS Specialist, Paul Bechtel & Associates, Inc. and Andrew Weinberg, Geoscientist, Texas Water Development Board

Presented at the 2011 Texas GIS Forum

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    Monitoring playa water resources using gis and remote sensing Monitoring playa water resources using gis and remote sensing Presentation Transcript

    • Estimating Water Volumes in High Plains Playa LakesGIS image classification and analysis
    • Playas in Texas• Dominant hydrological feature of High Plains• ~20,000 mapped playas• Important source of groundwater recharge• Stop-over points for migratory waterfowl• Used for irrigation, forage, and grazing• Over 50 years of studies
    • Playa Features• Wetland area defined by soil, Wetland area plants, and Water area hydrology• Many playas lie within larger topographic depression• Water area varies Topographic depression seasonally
    • TWDB Playa ProjectBackground Continued drawdown of High Plains Aquifer threatens agricultural economy of the Texas PanhandleProject Objectives 1. Determine volume and distribution of playa water resources 2. Determine timing and magnitude of recharge under current conditions 3. Assess playa modification strategies to increase recharge
    • Objective 1: Determine Volume and Distribution of Playa Water ResourceTwo strategies:• Field monitoring – Instrument and survey selected playas• Remote sensing – Estimate water resource region-wide
    • Field Monitoring
    • Field MonitoringPROs CONs• Tailored to project objectives • Time consuming• Continuous observations • Expensive• Access to subsurface • Continual maintenance,• Ground-truth remote/indirect recalibration observations • Access agreements • Extensive QC and data management
    • Remote SensingPROs CONs• Data available for free • Clouds• Regional coverage • Limited resolution• 30-year archive of imagery • Limited frequency of• Work with desk-top tools observations
    • ESTIMATING PLAYA WATER VOLUME USING REMOTE SENSING AND GIS METHODS
    • ESTIMATING WATER VOLUME A 3-Part Process1. CLASSIFY WATER AREAS IN PLAYAS USING REMOTE SENSING METHODS2. OBTAIN PLAYA WATER SURFACE ELEVATION AND BASIN TOPOGRAPHY USING GIS METHODS3. ESTIMATE PLAYA VOLUME USING GIS METHODS
    • PART 1CLASSIFY PLAYA WATER AREAS
    • CLASSIFY PLAYA WATER AREAS EVALUATE AVAILABLE RS IMAGERY• 21 Types of Remotely-Sensed Imagery were evaluated• 17 were eliminated due to: lack of current data, wrong scale, or simply not a good fit for the type of mapping inherent to the project• 4 selected for further consideration: Landsat-4, with the Thematic Mapper sensor (TM), Landsat-5 TM, and Landsat-5 Multi-Spectral Scanner (MSS), Landsat-7
    • CLASSIFY PLAYA WATER AREAS EVALUATE AVAILABLE RS IMAGERY (cont.)× Landsat-4 TM, decommissioned June 2001. (need current data) Landsat-5 TM: improved spectral separation and geometric fidelity, greater radiometric accuracy and resolution than the MSS sensor. Used to monitor changes in land surface over periods of months to years—a near perfect fit for this project!× Landsat-5 MSS: Landsat-5 TM better fit for this project.× Landsat -7: The Scan Line Corrector (SLC) in the ETM+ instrument failed in 2003; good data from 1999 – 2003.
    • CLASSIFY PLAYA WATER AREAS Obtain Landsat-5 TM ImageReadily available fromlandsat.gsfc.nasa.gov ORglovis.usgs.govUser friendly GUI allowsobtaining by coordinates,satellite row/path, or byinteractively selecting anarea of interest. https://glovis.usgs.gov
    • CLASSIFY PLAYA WATER AREAS Obtain Landsat-5 TM Image
    • CLASSIFY PLAYAS WATER AREAS Evaluate TM Spectral BandsBand Wavelength, µm Characteristics1 0.45 to 0.52 Blue-green. No MSS equivalent. Maximum penetration of water, which is useful for bathymetric mapping in shallow water. Useful for distinguishing soil from vegetation and deciduous from coniferous plants.2 0.52 to 0.60 Green. Coincident with MSS band 4. Matches green reflectance peak of vegetation, which is useful for assessing plant vigor.3 0.63 to 0.69 Red. Coincident with MSS band 5. Matches a chlorophyll absorption band that is important for discriminating vegetation types.4 0.76 to 0.90 Reflected IR. Coincident with portions of MSS bands 6 and 7. Useful for determining biomass content and for mapping shorelines.5 1.55 to 1.75 Reflected IR. Indicates moisture content of soil and vegetation. Penetrates thin clouds. Good contrast between vegetation types.6 10.40 to 12.50 Thermal IR. Night time images are useful for thermal mapping and for estimating soil moisture.7 2.08 to 2.35 Reflected IR. Coincides with an absorption band caused by hydroxyl ions in minerals. Ratios of bands 5 and 7 are potentially useful for mapping hydrothermally altered rocks associated with mineral deposits.
    • Landsat-5 TM Subscene, SE Quadrant, Floyd County (October 15, 2010)
    • Composite and Detail Views of Enlarged Landsat-5 TM Subscene, SE Quadrant, Floyd County (October 15, 2010)
    • CLASSIFY PLAYA WATER AREAS Single, Band-5 Selected• Initial evaluation indicated single-spectral Band 5 classification provided best results with minimal processing• Grid cells with a value of ≤60 indicate water area• Field verification scheduled Landsat-5 TM, Band 5
    • CLASSIFY PLAYA WATER AREAS Field Verification - 11 May 2011• Scheduled to coincide with Landsat-5 image acquisition• Cloud-free day• Visual inspection of playas on transect across study area• 30 Playas in corridor classified as wet, wet soil only, or dry• Attributes overlaid on Landsat imagery for further review. Location Map of all Field-Verified Playas
    • CLASSIFY PLAYA WATER AREAS Field Verification—Wet Playas DETAIL AREA Landsat-5 TM, Spectral Detail of Wet Playa Band 5 (Wet Playa)
    • CLASSIFY PLAYA WATER AREAS Field Verification—Wet/Dry Playas DETAIL AREA Landsat-5 TM, Spectral Detail of Wet/Dry Playa Band 5 (Wet/Dry Playa)
    • CLASSIFY PLAYA WATER AREAS Field Verification--Dry Playas DETAIL AREA Landsat-5 TM, Spectral Detail of Dry Playa Band 5 (Dry Playa)
    • CLASSIFY PLAYA WATER AREAS Create Final Footprints• Contour using Spatial Analyst: --input raster = Band 5 --contour interval = 60• Isolines ≠60 removed and non-playa water areas clipped• Remaining feature lines converted to polygons using Data Management Tools in ArcToolBox Wet Playa Footprints, October 15, 2010
    • PART 2OBTAIN PLAYA SURFACE ELEVATION AND BASIN TOPOGRAPHY
    • PLAYA SURFACE ELEVATION AND BASIN TOPOGRAPHY Evaluate Available Elevation Data• Five data-sets evaluated: National Elevation Dataset (NED), Shuttle Radar Topography Mission (SRTM), Digital Elevation Models (DEM), and Global 30-Arc- Second Elevation Dataset (GTOP030).• Major considerations included: seamless coverage, matching scale, current data, and easily accessible NED Data selected (http://seamless.usgs.gov) • regularly updated composite of the latest DEM • seamless • 10-meter resolution – best available for study area
    • PLAYA SURFACE ELEVATION AND BASIN TOPOGRAPHY NED (Floyd County, TX)
    • PLAYA SURFACE ELEVATION AND BASIN TOPOGRAPHY Obtain Playa Surface Elevations• Project elevation data to UTM using ArcINFO Workstation• Create Raster point file using ArcToolBox conversion tools• Associate maximum surface elevation with individual playa footprints using spatial join. However…• Extremely long processing times (11 hours!) when using the entire NED data set so an interim step was introduced• Spatial query used to extract points inside or near playas, then the spatial join was applied to the refined point data set (spatial join processing time now <2 hours).
    • PLAYA SURFACE ELEVATION AND BASIN TOPOGRAPHY Create Final Elevation Data SetSUMMARIZE ON PLAYA-IDTO OBTAIN MIN/MAXELEVATION VALUES
    • PLAYA SURFACE ELEVATION AND BASIN TOPOGRAPHY Min/Max Elevation Attributes now Associated with Wet Playa Footprints
    • PART 3ESTIMATE PLAYA WATER VOLUME
    • ESTIMATE PLAYA WATER VOLUME Work Directly with Raster DataTop Surface: Generated using Polygon to Raster basedon Max Grid Elevation valueBottom Surface: Obtained directly from projected NEDraster (no additional processing involved)Volume Method: Use Spatial Analyst CutFill
    • ESTIMATE PLAYA WATER VOLUME Inspect Tabular Results
    • ESTIMATE PLAYA WATER VOLUME Visually Inspect “0” Volume Area(s)
    • ESTIMATED WATER VOLUME, FLOYD COUNTY, TEXAS (OCTOBER 15, 2010) Final Results • Water identified in 741 of the 1,721 mapped playas in Floyd County • Water area = 18,395 acres (2.89% of Floyd County) • Water volume = 97,216,952 cubic meters or 78,815 acre- feet in Floyd County playas on October 15, 2010.
    • WHAT’S NEXT?Additional Method Validation and Volume Estimates
    • Next StepsMethod Validation • Playa surveys • Area-volume and depth- volume relationships • Water level observations • Compare with remote sensing Bivins Playa -Elevation - Area 250 200Area, acres 150 100 50 0 3238 3240 3242 3244 3246 3248 Elevation, ft msl
    • Method Validation• Accuracy of RS estimates limited by: – Image pixel size, pixel classification, and contouring – Local accuracy of NED surface – Landscape changes over time since underlying topographic data collected• Field data accuracy limited by: – GPS accuracy (~ ½ inch vertical for Trimble R6) – Number and distribution of grid points – Access limitations
    • Method Validation Floyd Crop Playa• Single Floyd County playa with field data for 2270500 970.2 10/15/2010 2270450 970.1 970 969.9 969.8 – RS volume estimate of 2270400 969.7 969.6 969.5 43,247 cubic meters 2270350 969.4 969.3 969.2 – Field volume estimate 2270300 969.1 969 968.9 of 51,218 cubic meters 2270250 968.8 968.7 968.6 based on 38 cm water 968.5 968.4 968.3 2270200 depth 968.2 968.1 968 – 16.9 relative percent 2270150 difference 340000 340050 340100 340150 340200 340250 340300 340350 340400 340450 0 50 100 150 200
    • Validation Data Set• Scale up to area ofone Landsat image tile• TWDB data • No TWDB playas in image area filled in 2011 • No data for 2010• TTU/ARS data • 16 playas monitored in 2010 • Look at images from 9 TTU/ARS Playa June, 25 June, 12 TWDB Playa August, and 15 October 2010
    • QUESTIONS